Barkley – like full debutants Declan Rice and Callum Hudson-Odoi – was starting due to injuries, and he took full advantage of his opportunity, inspiring the rampant Three Lions by having a hand in three goals.
Marko Vesovic's well-taken opener had England on the back foot early on, but they went into the break ahead thanks to Michael Keane's first international goal and an instinctive finish from Barkley, who set up the equaliser.
England's play became sloppy at times early in the second period but Barkley effectively ended Montenegro's chances just before the hour, before Harry Kane and Raheem Sterling wrapped up the victory to add to the 5-0 demolition of the Czech Republic at Wembley.
Although England controlled the early exchanges, Montenegro took the lead against the run of play in the 17th minute – Vesovic beating Jordan Pickford with a curling effort from 12 yards after playing the ball against Keane.
The England centre-back levelled at the half-hour mark, however, finding the bottom-right corner with a fine header from Barkley's free-kick.
Barkley was vital again as England took the lead eight minutes later, diverting Hudson-Odoi's slightly wayward shot in from close range.
Danijel Petkovic was helpless in the 59th minute as Sterling' cutback was knocked straight to Barkley by Stefan Savic, and the Chelsea man swept home from the centre of the area.
Kane got in on the act with 19 minutes to play, tapping a squared pass from Sterlin - who was released by Barkley - in from close range for his 17th goal in 20 England appearances under Gareth Southgate.
Manchester City star Sterling rounded things off in the 80th minute with a tidy finish following substitute Jordan Henderson's incisive pass.